Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities
Net loss	$ (268,113)	$ (226,505)	$ (137,125)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	1,924	1,311	1,542
Amortization of premium on investment securities	1,113	3,174	3,703
Stock-based compensation expense	30,362	22,858	9,333
Non-cash interest	61
Change in reserve for uncertain tax position		(365)
Unrealized loss on foreign currency forward contracts			114
Changes in operating assets and liabilities:
Receivables from collaborations	1,000	(943)	252
Prepaid research and development	9,677	(15,290)	(745)
Prepaid expenses and other current assets	378	1,001	(1,383)
Prepaid and other long-term assets	6,779	3,619	(15,559)
Accounts payable	4,308	(4,061)	10,763
Accrued compensation and employee benefits	(653)	2,054	893
Accrued research and development	(377)	11,650	(3,565)
Accrued and other liabilities	(892)	1,531	(261)
Deferred revenue	18,747	(9,569)	31,374
Other long-term liabilities	(769)	2,281	(42)
Net cash used in operating activities	(196,455)	(207,252)	(100,706)
Investing activities
Purchases of property and equipment	(1,864)	(4,746)	(1,629)
(Increase)/decrease in restricted cash (SRX Cardio)	163	(341)
Purchases of investments	(252,323)	(266,068)	(332,171)
Proceeds from sales of investments			2,603
Proceeds from maturities of investments	394,730	324,100	192,045
Net cash provided by/ (used in) investing activities	140,706	52,945	(139,152)
Financing activities
Proceeds from public offering of common stock, net of underwriters discount		272,216	175,185
Payment of public offering costs	(242)	(882)	(564)
Proceeds from issuance of common stock pursuant to equity award plans	1,683	11,948	4,978
Dividends to Noncontrolling interest (SRX Cardio)'s shareholders	(1,700)
Proceeds from long-term note payables	50,000
Proceeds from long-term obligation to Collaborator	8,000
Net cash provided by financing activities	57,741	283,282	179,599
Net increase (decrease) in cash and cash equivalents	1,992	128,974	(60,259)
Cash and cash equivalents at beginning of year	186,488	57,514	117,773
Cash and cash equivalents at end of year	188,480	186,488	57,514
Noncash investing and financing activities:
Net change in accrued offering cost	$ (238)	238
Net change in accounts payable related to purchase of property and equipment		$ 5	$ 89